Current-suppressor



Dec. 13, 1932.

w. H. T. HQLDEN CURRENT SUPPRESSOR Filed April 1v, 1930 IlllLl/qllllvlll llllll INVENTOR BY Wmamm ATTORNEY Patented Dec. 13, 19732 UNITED STATES PATENT OFFICE WILLIAM H. T. HOLDEN,`OF BROOKLYN, NEW `YORK, vASSIGrNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, `A. CORPORATION 0F NEW YORK CURRENTfSiUPPRESSOR Application mea April 1*7,

-More particularly, this invention relates to amplifying systems arranged so as to suppress currents of particular frequencies.

This invention will findi application in radio or carriersystems generally, Where it is desired to eliminate the effect of current of some particular frequency. yThis invention will find special application in connection with a balanced modulating systemV which is arranged to eliminate the carrier current employed in the process of modulation, in which there may be a carrier leak.

The invention may be broadly considered as comprising two electron tubes which may forman amplifier having two parallel paths to which the same current or currents are transmitted in the same phases and from which these currents are independently obtained, displaced substantially 180 degrees in phase. If these amplifying paths have equal gains, the transmitted current or currents will exhibit equal and opposite effects. If these currents are impressed upon a common circuit, their effects will be neutralized, as is well understood in the art.

This invention will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing in which Figure l represents one embodiment of the invention given merely for the purpose of illustration, andFig. 2 represents a group of curves illustrating certain of thev principles involved in the invention.

Referring to Fig. l of the drawing, the reference character O2 represents an input circuit which may be connected to a source supplying currents of a plurality of frequencies, one of which it is desired to suppress. The circuit Ol is connected to the primary winding L1 of a transformer T1; lThe secondary winding L2 of this transformer is connected in a local circuit with a resistance R2 and a condenser C0. The winding L2 is connected in another local circuit with a resistance R2 and a winding L0. A potentiometer P1 bridges the condenser Co and another potentiometer-P2 bridges the winding L0.

, winding `serieswith a battery B3.

1930. serial No. 445,143.

The reference characters V1 and V2 represent4 two electron tubes, each of which may be of the three-electrode type. The filaments of thesetubes are connected in parallel relationship with respect to abattery B1. The grid elecrode of the tube V1 is connected to the movable arm of the potentiometer P1 and the grid electrode of the tube V2 is connected to the movable arm of the potentiometer P2. A` battery B2 is connected between the junction `common tolpotentiometers P1 ments of tubes V1 and V2 and this battery is employed forV the purpose of biasing the grid electrodes of tubes V1 and-V2 at suitable negativeY potentials with respect to their corresponding iilaments for good amplifying action.

The reference character T2 designates a transformer having primary windings L3 and L4 and a secondary winding L5. Primary L3 is connected between the plate electrode and the lilament of the tube V1 in The winding L4 is connected between the plate electrode and the filament of the tube V2, also in series with the battery B3. This battery is employed for the purpose ofV maintaining the of tubes Vl Vand V2 at suitable positive potentials with respect to the corresponding `filaments. The currents Howing through windings L3 and L,i from battery Ba will be `oppositely directed. The secondary winding L5 is connected to an output circuit O2.

`The condenser C0 will receive a current ,fromsource `O1 through the transformer T,L

which will lead the impressed voltage 90 degrecs.V Current will `be transmitted through thepotentiometer P1 which will be in phase with the impressed voltage.v Inasmuch as the condenser@0 and the potentiometer P1 are connected in parallel relationship, the resultant current vwill lead the impressed voltage land this resultant current will be the `vectorial sum of the currents transmitted through condenser C0 and potentiometer Current through the winding Lo will lag Abehind the impressed voltage by a phase angle of 90degrees while the potentiometer and P2l and thejunction common to the ilaplate electrodes P2 will receive current in phase with the impressed voltage. Since winding L0 and potentiometer P2 are connected in parallel relationship, the resultant current will lag behind the impressed voltage and the magnitude of the resultant current will be the vectorial'` sum of the currents through winding L0 and potentiometer P2.

It is to be noted that condenser C0 and winding LO ai'e bridged across two parallel circuits which are supplied with currents of the same phase. These circuits also include tubes V1 and V2, respectively.

The employment of reactive elements in association with the tubes V1 and V2 renders their transmission-frequency characteristics non-linear. Thus, currents of all frequencies will not be equally transmitted by these tubes. Y If it be desired that the currents transmitted to windings L2 and L2 of transformer T2 be exactly 180 degrees apart in phase, it may be necessary to connect a phase correcting arrangement between the plate electrodes Vof tubes V1 and V2 and the windings L3 and f L2.- One form of phase correcting network which may be employed in this connection will include a winding of small and variable inductance connected between the plate electrode of tube V1 and the upper terminal of winding L3, a winding of large inductance connected between the plate electrode of tube V2 and the lower terminal of winding L4 and a variable condenser in shunt with the winding of large inductance.

The grid electrodesl of the tubes V1 and V2 are so connected that impressed currents will be exactly in phase with each other if the reactive elements-C0 and L0 as well as all of the phase correcting elements be omitted from consideration. Moreover, the plate electrodes of the tubes V1 and V2 are so connected 'that the phases of the currents derived from these tubes will be exactly 180 degrees displaced with respect to each other. Therefore, if the potentiometers P1 and P2 are adjusted to apply equal amplitudes to the grid electrodes of the tubes V1 and V2, there will be no current in the output circuit O2 at any frequency. This is due to the interaction in the windings L3 and L4 of the transformer T2 of the equal and opposite currents derived from the tubes V1 and V2.

The addition of the reactive elements C@ y and L0 has two eects. First, these elements cause the gains of tubes V1 and V2 to vary with frequency, as will be shown hereinafter Yin connection with the description of Figure 2.. Second, these reactive elements introduce phase shifts which also vary with the frequency of the current impressed thereon and these phase shifts will 4vary oppositely. That is to say, the phase shift in the branch RlOOP1 will increase with frequency, reaching a maximum of 90 degrees, while the phase in the branch R2L0P2 will decrease with frequency,

Leeds@ reaching a value of zero at its limit. Thus, there will be a phase displacement of less than 90 degrees between the two paths so that currents flowing in the plate circuits of the tubes V1 and V2 will no longer be in exact phase opposition in the windings L3 and L2. However, the introduction of the phase corv recting elements shown in the drawing makes it possible to adjust the phase difference to 180 Vdegrees for any particular frequency. At the same time, the gain may be adjusted by means of potentiometers P1 and P2 so that the amplitudes of the currents of the particular frequency for which suppression is desired, will be equal. Tf the amplitudes of the currents of the particular frequency flowing in windings L3 and L4 are equal and their phases 180 degrees apart, no current of the particular frequency will reach the output circuit O2.

Fig. Q shows various curves plotted so that the-abscissac represent frequencies and the ordinates gains. The curve l represents changes in the gain of the tube V1 for currents of different frequencies while the movable arm of th-e potentiometer P1 is maintained stationary. Tt is to be noted that the gain decreases with frequency and this is due to the employment of an element exhibiting capacitive reactance in shunt across the transmission path which includes the tube V1. The curve crepresents changes in the gain of tube V2 for currents of different frequencies while the movable arm of potentiometer P2 remains stationary. Here the gain increases` with frequency and this is due to the employment of an element of inductive reactance in shunt across the transmission path which includes the ytube V2.

Curves c and d will coincide at a point at which the gains of tubes V1 and V2 will be equal. The abscissa corresponding to the point of coincidence will designate the frequency of the current which will be substantially suppressed and will not be found in the output circuit O2.

The dot` and dash curve e will represent the resultant changes in the gain for currents of different frequencies. The slope of this curve will be 90 degrees at that frequency corresponding to the point at which curves c and d coincide.

The dashed curve f will designate changes in the gain of the tube V1 for currents of `dii'ferent frequencies when the movable arm of potentiometer P1 is raised so as to increase the gain of tube Vl by, for example, l decibels, The dashed curve f/ will represent changes in the gain of tube V2 for currents of different frequencies when the movable arm of the potentiometer P2 is lowered so as to reduce the gain of the tube by, for example, 4 decibels. Curves f and g will coincide at a point at which the gains of tubes V1 and V2 will be equal and the abscissa determined by this soA point will designate the frequency of current at which suppression will occur. The double dot and dash curve it will represent the resultant of curves f and g and it will be noted that curve L has a slope of 90 degrees at a point having the same abscissa as the point of coincidence of curves f and g.

It will be apparent that the two transmission paths including the tubes V1 and V2 may be adjusted by potentiometers P1 and P2, respectively, so that the amplitudes of the currents of a particular frequency trans mitted by these paths will be equal in order that the effect of these currents may be substantially suppressed. If the movable arm of the potentiometer P1 is maintained stationary, the frequency at which suppression will occur may be increased by raising the movable arm of potentiometer P2 and decreased by lowering the movable arm of this potentiometer. Similarly, if the movable arm of potentiometer P2 is maintained stationary, the frequency at which suppression will occur may be raised by lowering the movable arm of potentiometer P1 and lowered by raising the movable arm of this potentiometer. So it will be understood that the characteristics of the transmission paths may be changed so as to produce suppression at any desired or predetermined frequency.

While this invention has been shown in one particular embodiment merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organiza-tions without departing from the spirit of the invention and the scope of the appended claims. Y

What is claimed is:

l. A current suppressing system comprising, in combination, a first potentiometer, a condenser bridging said first potentiometer, a second potentiometer, a winding bridging said second potentiometer, and two amplifiers connected, respectively, to said potentiometers, said amplifiers being connected in opposition, said potentiometers controlling the frequency of the current to be suppressed.

2. The combination of two parallel vacuumtube amplifiers, means for supplying currents to said amplifiers so that these currents may be in phase with each other, means for separately deriving from said amplifiers currents which are displaced about 180 degrees in phase with respect to each other, potentiometric means for rendering equal the amplitudes of the currents of a particular frequency transmitted by said amplifiers, and a circuit coupled to both amplifiers.

3. The combination of an input circuit divided into two branches, a condenser shunting one branch of said input circuit, a winding shunting the other branch of said input circuit, a iirst potentiometer shunting said condenser, a second potentiometer shunting said winding, two electron tubes each having grid, filament and plate electrodes, the grid and filament electrodes of on-e of the tubes being connected to the first potentiometer and the corresponding electrodes of the other tube being connected to the second potentiometer, a transformer having three windings one of which is connected between the plate and filament elec trodes of one of the tubes and another to the corresponding electrodes of the other of the tubes, and an output circuit connected to the third winding of said transformer.

In testimony whereof, I have signed my name to this specification this 15th day of April, 1930.

VILLIAM H. T. HOLDEN. 

